1. Field of the Invention
The present invention relates to a thin film transistor (“TFT”) substrate, a method of manufacturing the TFT substrate, and a display apparatus having the TFT substrate. More particularly, the present invention relates to a TFT substrate capable of preventing a variation of a storage capacitance, a method of manufacturing the TFT substrate, and a display apparatus having the TFT substrate.
2. Description of the Related Art
In general, a TFT substrate is used for a circuit substrate to individually drive a plurality of pixels in a display apparatus such as a liquid crystal display (“LCD”) apparatus, an organic electro luminescence apparatus, and so on.
A voltage is charged in the pixels of the TFT substrate during a predetermined time, and the voltage charged in the pixels is held by a storage capacitor during one frame.
A structure of the TFT substrate is classified into an organic layer structure and a non-organic layer structure. The TFT of an organic layer structure employs an organic layer to planarize a surface of the TFT substrate, whereas the TFT of a non-organic layer structure lacks the organic layer of the organic layer structure. In the TFT substrate of the non-organic layer structure, the storage capacitor is defined by a gate line, a pixel electrode, a gate insulating layer, and an inorganic layer. The gate insulating layer and the inorganic layer are disposed between the gate line and the pixel electrode. However, the TFT substrate of the organic layer structure further includes the organic layer disposed on the inorganic layer. In the TFT substrate of the organic layer structure, a capacitance for the storage capacitor decreases because the organic layer acts as a dielectric substance. However, when an overlapped area between the gate line and the pixel electrode increases in order to increase the capacitance for the storage capacitor, an opening ratio of the TFT substrate decreases. Thus, the storage capacitor defined by the gate line, a data line, and the gate insulating layer has been developed for the TFT substrate of the organic layer structure.
In general, the TFT substrate is manufactured via a five-mask process or a four-mask process. However, in the TFT substrate manufactured via the four-mask process where the data line and an active layer are simultaneously patterned, the active layer remains under the data line. The storage capacitor is, therefore, formed in a metal oxide semiconductor (“MOS”) structure in the four-mask process.
However, a capacitor of the storage capacitor having the MOS structure periodically varies according to a polarity of a voltage applied to the storage capacitor. As a result, a display defect such as a flicker or an afterimage occurs on a screen of the LCD apparatus.